In recent years, HSUPA (High-speed Uplink Packet Access) has been established as the standard for high-speed packet communication in the upward direction, and the application of HSUPA to a cellular system provided with a base station for managing at least one cell for providing a wireless communication service such as a W-CDMA (Wideband Code Division Multiple Access) system is now being investigated. In order to design a system that satisfies the needs of a wireless communication service as prescribed by this HSUPA, the throughput of user data (hereinbelow referred to as “user throughput”) of the designed system must be estimated and verified.
In a system that conforms with HSUPA, user throughput fluctuates instantaneously because a scheduling process for carrying out data transmission according to the control of transmission power and the order of priority and an adaptive data transmission process for adaptively controlling the degree of data multiplexing are implemented in accordance with fluctuations in the uplink reception quality in the base station. As a result, the HSUPA process must be simulated in detail over a long time period and at high time resolution to accurately estimate user throughput.
In an actual cell, user terminals that use dedicated channels that are allocated to each user terminal to perform uplink communication coexist with user terminals that use HSUPA channels to perform communication to transmit HSUPA data, and this state must be assumed to estimate the user throughput.
As a result, in a throughput estimation system of the related art, the reception quality of each channel is estimated based on various setting values that are applied as input by operators, and the user throughput is estimated by simulating the processes of the cellular system including the upper-layer processes in a state that is closer to the actual state. Such simulation that includes these upper-layer processes is referred to as “system-level simulation.”
FIG. 1 shows an example of the procedure of a system-level simulation when HSUPA channels and individual uplink channels coexist.
The throughput estimation system shown in FIG. 1 can be realized by a computer (system-level simulator 300) in which programs for simulation are installed.
As shown in FIG. 1, the base station configuration, the traffic volume of the HSUPA channel, and the traffic volume of a dedicated channel used at a user terminal are entered as setting values into system-level simulator 300 by an operator. System-level simulator 300 estimates the reception quality of the HSUPA channel and dedicated channel based on the base station configuration or the traffic volume of each channel and executes the above-described system simulation to estimate the user throughput for each channel.
The received SIR (Signal to Interference power Ratio), which is the ratio of the received power to the interference power, is normally used for the reception quality of each channel. The base station configuration is information indicating the state of the base station, and includes information such as: the location of the base station; the maximum transmission power; the pattern or gain of the antenna; the antenna bearing; the antenna tilt; settings information for scheduling processes; the Target RTWP (Received Total Wideband Power), which is the target total reception power in the base station that is used in the transmission power control of user terminals; the Target SIR of the DPCCH (Dedicated Physical Control CHannel) that is used as the target SIR during HSUPA channel reception in the base station; the target SIR that is the target SIR during dedicated channel reception in the base station; the NF (Noise Figure) of the reception device provided in the base station; and thermal noise Nt.
The procedure of the throughput estimation system shown in FIG. 1 is next described.
System-level simulator 300 first arranges a user terminal in a random position and causes the user terminal to move. Traffic is generated according to the traffic volume of the HSUPA channel and dedicated channels that were entered as input by the operator in the user terminal that is in motion.
Next, system-level simulator 300 both controls the transmission power in the user terminal and calculates the instantaneous interference power from other user terminals in the cell and user terminals in other cells to calculate the uplink reception quality of each channel in the base station.
System-level simulator 300 then carries out a scheduling process and adaptive data transmission process based on the reception quality of each channel and calculates the instantaneous user throughput of each channel.
System-level simulator 300 repeats the above-described calculation processes every 2 ms, which is the processing period prescribed by HSUPA, and determines whether or not the calculation processes have been repeated at least a predetermined number of times that is determined in advance for obtaining the desired estimation accuracy. If the calculation processes have been repeated at least the predetermined number of times, the average value of the user throughput for each identical position of the user terminal in each repeated process result is calculated. If the above-described calculation processes have not been repeated at least the predetermined number of times, the user terminal is caused to move and the processes up to that point are repeated.
Finally, the averaged HSUPA channel user throughput (hereinbelow referred to as “HSUPA throughput”) and the user throughput of dedicated channels (hereinbelow abbreviated as “dedicated channel throughput”) for each position of the user terminal are supplied as output.
To obtain an estimation result of user throughput having high reliability by a statistics process, the above-described calculation processes of a 2-ms unit must be continuously executed for approximately one hour or more, and a highly precise estimated value of user throughput is obtained by executing this repeated process. However, continuous execution of the above-described calculation processes of 2-ms units for one hour or more results in a vast amount of calculation and a lengthy processing time.
This lengthening of the processing time becomes particularly problematic when investigating an ideal base station configuration that satisfies user throughput. The problem arises because the above-described system-level simulation is executed each time the base station configuration is altered, and the lengthy processing is repeated over and over, making the total time of the repeated processing extremely long.
The above-described lengthening of processing is also problematic when estimating the geographical distribution of the HSUPA throughput according to a plurality of states of a cellular system (hereinbelow referred to as “scenarios”) in which the state of mixing of HSUPA channels and dedicated channels differs. This problem arises because the above-described series of processes is repeated for each assumed scenario, resulting in a massive total processing time.
However, Monte Carlo simulation is known as a conventional method of estimating dedicated channel throughput whereby snapshots are modeled to carry out simulation repeatedly to find an estimated value of throughput. A snapshot is information indicating the state of a cellular system (user terminal positions, the generation or non-generation of traffic, the amount of interference power that arrives from other cells, etc.) that is obtained at any instantaneous time point.
A dedicated channel does not experience instantaneous fluctuation in uplink user throughput according to reception quality as does a HSUPA channel, and user throughput can therefore be estimated in a relatively short process time interval. As a result, Monte Carlo simulation is frequently used in the estimation of user throughput of dedicated channels. For example, Japanese Laid-Open Patent Publication No. 2003-224515 discloses a simulation method in which Monte Carlo simulation snapshots are corrected.
The above-described Monte Carlo simulation can be used when estimating not only the user throughput of a dedicated channel but also HSUPA throughput. However, as described hereinabove, user terminals that use dedicated channels to communicate and user terminals that use HSUPA channels to communicate coexist in an actual cell. A method that can precisely estimate HSUPA throughput using Monte Carlo simulation in a state in which traffic of dedicated channels and HSUPA channels coexists has yet to be established.
In the case of a cellular system that is made up of a plurality of cells, the influence of HSUPA channel traffic generated by user terminals in other cells upon a user terminal in the cell of interest, i.e., the interference power value from other cells (hereinbelow referred to as “other-cell HSUPA interference power value”) must be considered when estimating HSUPA throughput, but when the other-cell HSUPA interference power value is modeled for each snapshot, the problem occurs that the other-cell HSUPA interference power value undergoes great fluctuation in each snapshot. As a result, the number of repeated processes of the Monte Carlo simulation must be greatly increased when averaging the fluctuation in the other-cell HSUPA interference power value, raising the problem of lengthy processing time of the Monte Carlo simulation.